The purpose of a bearing protector is to prevent the ingress of fluid, solids and/or debris entering a bearing arrangement and thereby prevent the failure of the bearing. Bearing protectors generally fall into two categories: repeller or labyrinth bearing protectors; and mechanical seal bearing protectors.
A repeller bearing protector includes a component which is mounted for rotation about a shaft and axially fixed in relation thereto. For example, the shaft may be that of a pump or other piece of rotating equipment. The protector includes a static component which is also axially fixed and is butted or secured to the stationary part of the equipment.
The rotating component typically has a complex outer profile which is located adjacent to an inner complex profile of the stationary component. Together these complex profiles provide a tortuous path preventing the passage of the unwanted materials.
A repeller bearing protector normally works only during the operation of the equipment. When the equipment is static, the complex labyrinth design is unable to hold a fluid level which, in horizontal application, is at a higher radial level than the inlet position of the protector.
A mechanical seal bearing protector overcomes the static limitations of the labyrinth design by the use of two opposing seal faces. Such a protector includes a “floating” component which is mounted for axial movement about the rotary shaft of; for example, a pump and a “static” component which is axially fixed and is typically secured to a housing. The floating component has a flat annular end seal face which is directed towards a corresponding seal face of the static component. The floating component is urged towards the static component to close the seal faces together to form a sliding face seal, usually by means of one or more spring members. The rotating component, which in practice could be either the floating or the static component, is referred to as the rotary component. The other component does not rotate and is referred to as the stationary component. A rotary seal is one whose floating component is rotary and, in a stationary seal, the floating component is stationary. If the sliding seal between the rotary and the stationary components is assembled and pre-set prior to despatch from the manufacturer, the seal is termed a “cartridge seal”. If the rotary and the stationary components are despatched in unassembled condition by the manufacturer, the seal is termed a “component seal”.
Mechanical seals are used in all types of industries to seal a variety of different process media and operating conditions. The term “inboard” defines the area adjacent to the process media and the term “outboard” defines the area adjacent the atmospheric side.
Desirably, a mechanical seal bearing protector prevents the ingress of fluid etc. irrespective of the direction of shaft rotation. Furthermore, it is also desirable that the bearing protector does not generate a spark during dynamic operation.
Bearing protectors are generally very compact at least as far as their axial length is concerned. Typically they are used to replace so-called lip seals and are fitted into spaces previously occupied by such seals. In order to maintain a compact axial length, the floating component may be energised by one or more magnets in either attracting mode (U.S. Pat. No. 5,078,411 Geco) or repelling mode (EP-0105616 Burles).
Geco discloses a rotary component seal which has a magnetic stationary member and a rotary member with more than one magnet spaced around the periphery of the component. The rotary and stationary members are attracted to one another by the magnetic force. The stationary seal face is limited to a magnetic material and is adjacent to the sealing surface in contact with the sealed medium. Accordingly, metallic particles in the sealed medium are attracted to the seal face. Soft seal faces such as carbon can, as a result, be easily damaged. Furthermore, the strength of attraction between the relatively rotating members is limited to the axial extent of non-magnetic material between the two magnets. If the distance is too large, the magnetic attraction will be sufficient to hold the seal faces together. If the distance is too small, flux migration can occur.
U.S. Pat. No. 4,795,168 (Adams et al) shows another configuration in which two relatively rotating seal faces are attracted to one another by a magnetic force. This arrangement is also vulnerable to flux migration between the two relatively rotating members.
U.S. Pat. No. 5,730,447 (Dawson et al) again discloses a rotary component seal having a magnetic stationary member and a rotary member with magnetic elements spaced around the periphery of the component. Again the arrangement is vulnerable to flux migration between the two relatively rotating members. Buries discloses two mechanical seal faces whose relative axial position is maintained by at least one set of repelling magnets which replace a conventional compression spring. The repelling forces act to separate stationary members, one of which is fixed to, for instance, the housing of the equipment and the other of which is axially floating. Such an arrangement, requiring both fixed and floating stationary members is not appropriate for bearing protectors.